This invention relates to flame retardant compositions containing at least one tetrahalophthalate ester and a polybutylene terephthalate (PBT) resin. Additionally this composition may also contain one or more brominated and/or chlorinated compounds in an amount to provide additional flame retardancy to the PBT resin. This invention also comprehends the method of improving the flame retardancy and melt processability of the polybutylene terephthalate resins by using these tetrahalophthalate esters alone or in combination with one or more bromine and/or chlorine compounds.
Polybutylene terephthalate resins are known in the art as a class of thermoplastics that are characterized by excellent properties such as thermal stability, good resistance to brittleness, low friction and wear, chemical resistance, etc. In general, they are prepared by the polycondensation of terephthalic acid or a diester of terephtahalic acid, such as dimethyl terephthalate (DMT), with 1,4 butanediol. U.S. Pat. Nos. 2,645,319; 3,047,539; 3,953,394; and 4,024,102 describe in detail the preparation of PBT, the teachings of which are incorporated herein by reference.
The PBT Resins are useful in many commercial applications including formation of fibers, film, and molded articles. Other applications include mechanical components, electrical parts, motor parts and the like.
The use of brominated and/or chlorinated compounds by themselves or in combination with other materials such as organic phosphates, antimony compounds, etc. as flame retardants for polybutylene terephthanlate are well known in the art and are exemplified by U.S. Pat. Nos. 3,953.394; 4,024,102; 4,079,034; 4,105,622; 4,165,309; 4,180,496; 4,229,552; 4,284,550; 4,546,126; 4,456,719; 4,525,529; 4,546,139; 4,602,111; and 4,612,344. The teachings of the aforesaid patents are incorporated herein by reference.
Tetrahalophthalate esters have been used as flame-proofing materials. For example, U.S. Pat. No. 4,098,704 describes the use of these materials as textile finishing agents. U.S. Pat. Nos. 4,298,517 and 4,397,977 disclose these compounds as flame retardants for halogenated resins.